This invention relates to a method and system for operating a telephony service, and in particular to a call management protocol on a telephony network.
A substantial number of users of modern telephone networks make use of prepayment mechanisms to pay for their calls on a network. For example, users of a conventional fixed-line telephone network who use public telephones will typically use prepayment cards which store a credit value which is reduced according to the cost of calls made. Users of mobile networks who make use of prepaid airtime typically purchase an airtime recharge voucher which has a unique code. The user contacts the network and enters the code, and the balance of the user's prepaid airtime is increased accordingly. As the user makes calls, the balance is reduced accordingly.
In either case, once the credit value or prepaid airtime is exhausted, the user is prevented from making further use of the network and in particular making telephone calls until a new prepayment card is obtained (or the existing card is replenished with a further credit value) or further prepaid airtime is “loaded” on the network.
With the advent of modern telephone networks and, more recently, cellular networks with enhanced functionality, it is now possible to modify existing network call management protocols to deal with calls from callers having no airtime or insufficient airtime to make a call.